New engine setup & oil pressure
Turbo Mini Forums

When setting up a new turbo engine to run in, what kind of AFR on the wideband should I be aiming for at idle? Currently it's set to around 14.7, but am I right in thinking really that's too rich at idle, and that really is the ideal figure to aim for under load?

Also, what oil pressure should be aiming for at idle, cold and hot? I'm getting oily smoke at the moment, and someone suggested it may be the oil pressure is too high for the GT17?

1994 Mini Mayfair, 1330, Mspd Ph2 cam, Benross turbo head, 9:1, GT1752, TT Intercooler, MegaJolt, BMW M3 leather seats.

14.7 is is fine for idle, either side and the hydrocarbons increase.as per the chart below.

oil pressure, as long as you have about 20+ on idle its fine, actually less is fin, but on a new engine i'd expect 30-40psi hot at idle.
at speed you dont wasnt it too high, 50-55 psi max with a turbo IMO,

OK thanks. At around 14.7 idle it seems to be running very rich when revved a little, and is spluttering lots. Running a BDD needle.

Will have to have a look tomorrow night. Could it be fuel pressure set too high? Think it's set at 4psi idle at the moment.

1994 Mini Mayfair, 1330, Mspd Ph2 cam, Benross turbo head, 9:1, GT1752, TT Intercooler, MegaJolt, BMW M3 leather seats.

possibly, although it would probbably richen up until it stalled at idle if the pressure was too high, but at 4 psi, probablu worth backing it off a little as its at the top end of what the SU will stop.

I take it youe getting the 14.7 from a wideband Gauge?

if its richening up too much with a throttle blip ( it should do a bit) then the dashpot oil is likly a bit thick, or maybe the spring too heavy, or even the dashpot sticking.

basic SU function.... the dashpot slides up with increasing airflow and moves the needle so the fuel flow increases, the spring has an effect on this by "increasing" the venturi effect by creating more of a restriction, a stronger spring will make the fuel get richer through out the range. on top of this the oil in the dashpot restricts furthur increasing the fueling more, acting as an accellorator pump jet,

OK, cheers. What fuel pressure do most run at idle?

1994 Mini Mayfair, 1330, Mspd Ph2 cam, Benross turbo head, 9:1, GT1752, TT Intercooler, MegaJolt, BMW M3 leather seats.

3-4 psi mate, think Shaunas sits around 12 afr at full chat from what i can remember

14.7 is a bit lean at idle for an A series. Ok for fuel injected modern cars. 13.8 is better. If your air fuel is too rich elsewhere up the rev range then you need a different needle profile

Edited by dazibee on 3rd Sep, 2016.

fuel pressure will have zero effect on your AFR at any point; unless:

1) It's so high that it exceeds the hold off pressure of the needle valve in the float bowl. This floods fuel into the engine un-metered and the car stops/floods

2) The pressure is not rising sufficiently on boost to fill the float bowl. This will result in emptying the float bowl and the car will stop (until the float bowl empties it will run fine).

Have you set the timing? I find that idle on a turbo car can be quite lean 17:1 as the cam profiles are 'soft' and compression is low.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Timing is megajolt controlled, using standard Metro turbo map for now.

I'll get a video tonight of how it's running.

1994 Mini Mayfair, 1330, Mspd Ph2 cam, Benross turbo head, 9:1, GT1752, TT Intercooler, MegaJolt, BMW M3 leather seats.

And are you using a wideband to check AFR?

It's worth checking the timing with a strobe.

In the 13's at last!.. Just

Yes mate, brand new AEM uego 30-4110.

Will check timing with a strobe, make sure the bracket/trigger wheel hasn't moved.

1994 Mini Mayfair, 1330, Mspd Ph2 cam, Benross turbo head, 9:1, GT1752, TT Intercooler, MegaJolt, BMW M3 leather seats.

OK, so what was happening was that when the throttle was blipped, it suddenly went very lean and spluttered. Had to run very rich at idle (choke out) to make it drivable.

So, we've added a second carb spring and it's now stopped leaning off when blipped. Set the AFR to around 12.5-13 at idle and it ran much better.

However, when putting the engine under a bit of labour (less than half throttle still) at around 1500rpm it goes round to about 15.5-16. Too lean?

When it gets to 2000rpm and you can hear the turbo start to spool, it goes back to around 13.

Even revved stationary now, it didn't seem to lean off until I let off the throttle where it goes lean and stays there for a second or two.

Check the video:
https://youtu.be/rreK9qgX2U4

1994 Mini Mayfair, 1330, Mspd Ph2 cam, Benross turbo head, 9:1, GT1752, TT Intercooler, MegaJolt, BMW M3 leather seats.

Ok. Set the idle mixture to 13.8
You can do the following without driving the car, rev and hold it at 1500 revs, after five seconds write down what afr reading you have. Do the same every 500 rpms until 5500. You will now know where you are for all your cruise needle positions.
Check out a good thread on here about polishing su needles. dont drive it on boost until you sort out the cruise. You are looking for 13.8 ish afr when cruising. Next job is to adjust the needle to cover acceleration and boost

If you are still running in you might not to rev as high as 5500 though

Mine seems happy very lean at idle. Is there a danger to damaging it if it's lean at idle? I didn't think there would be

My build thread..

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=542985

No damage i dont think, but more difficult to get the rest of the needle correct during the transition from idle to acceleration/ cruise.

It goes to 10 when I floor it at 10psi and it's about 14 or 13 at part throttle.

I've got a standard bdd in there with a high bpost spring. Green I think. And some thick transmission oil. Maybe I'm just lucky lol. Need to get to the rollers soon though to see if it can be improved.

My build thread..

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=542985

OK, thanks for that, I'll have a go, but won't go to 5500.

I did block off the part throttle lean off pipes today, and it's now running much better at low revs. It does now feel though at around 3500 , with boost/vacuum gauge at 0 (I.e. starting to boost, but not showing any positive psi yet) it really hesitates. It's not going lean though, if anything it goes rich - around 10-10.5.

1994 Mini Mayfair, 1330, Mspd Ph2 cam, Benross turbo head, 9:1, GT1752, TT Intercooler, MegaJolt, BMW M3 leather seats.